1. Field of the Invention
The present invention relates to a mobile communication method which is performed by a radio network controller, a first exchange and a second exchange which manages one location registration area.
Also, the present invention also relates to a radio network controller which can be used in the mobile communication method.
2. Description of the Related Art
Conventionally, a mobile communication system in which a location registration area is managed by a plurality of exchanges so that processing load in each exchanges can be dispersed is known. Referring to FIGS. 1A and 1B, this type of mobile communication system will be explained.
In this mobile communication system, as shown in FIG. 1A, a radio network controller RNC is connected to a first exchange for a packet switched service (SGSN: serving GPRS support node) #1 and a second exchange for a packet switched service (SGSN) #2, which manage a same location registration area via predetermined interfaces (e.g. Iu-flex interfaces).
When receiving a location registration request from the mobile station UE under the control of the radio network controller RNC, the radio network controller RNC determines an SGSN to which location registration of the mobile station UE is performed, in accordance with the status of load in each SGSNs.
The radio network controller RNC transfers the location registration request from the mobile station UE to the determined SGSN.
In FIG. 1A, the location registration of the mobile station UE #1 is performed to the first SGSN #1, and signals for each type packet switched service are transmitted via the first SGSN #1.
On the other hand, the location registration of the mobile station UE #2, which is located in the same location registration area as the mobile station UE #1, is performed to the second SGSN #2, and signals for each type of packet switched service are transmitted via the second SGSN #2.
However, in the conventional mobile communication system, there has been a problem in that, in the case where congestion or failure occurs in one of a plurality of SGSNs managing the same location registration area, not only mobile stations UE which has performed the location registration to the SGSN but also mobile stations UE which has performed the location registration to other SGSNs fails to transmit signals for each type of packet switched service to the registered SGSNs, that is, those mobile stations UE cannot used the packet switched services in that situation.
Specifically, as shown in FIG. 1B, in step S1, congestion or failure occurs in the first SGSN #1. In step S2, the first SGSN #1 transmits a state signal to the radio network controller RNC for notifying the occurrence of the congestion or the failure.
In step S3, the radio network controller RNC broadcasts an access restriction signal, which restricts accesses to the packet switched service domain, to the mobile stations UE.
Here, in the conventional mobile communication system, the radio network controller RNC cannot specify the first SGSN #1 where the congestion or the failure occurs in the access restriction signal.
Therefore, in step S4, the mobile station UE #1 stops transmitting signals for each type of packet switched service addressed to the first SGSN #1 in accordance with the received access restriction signal.
In step S5, the mobile station UE #2 also stops transmitting signals for each type of packet switched service addressed to the second SGSN #2 in accordance with the received access restriction signal.